1. Field of the Invention
The present invention relates to an exposure apparatus used in manufacturing a device having a fine pattern, such as a semiconductor device.
2. Description of the Related Art
Semiconductor manufacturing systems perform multiple processes on a wafer, and each process is performed in a state controlled so that an environment appropriated for the process is maintained. However, since environments appropriate for apparatuses vary with one another, it has become necessary to control an environment around the wafer during each of the processes and conveyance the wafer.
In exposure apparatuses for transferring a fine pattern, such as a circuit pattern, to a semiconductor wafer or a substrate, such as a substrate used for a liquid crystal display, a finer transfer pattern and an improved throughput are required. To obtain the finer transfer pattern, it is necessary for an exposure apparatus to reduce the wavelength of exposure light. Therefore, in addition to an exposure wavelength of an I line of 365 nm, recently, a krypton-fluoride (KrF) excimer laser of 248 nm and an argon-fluoride (ArF) excimer laser of 193 nm have been developed. For further finer patterns, development of a fluorine (F2) excimer laser of 157 nm and extreme ultraviolet (EUV) light is required.
However, because exposure light with a short wavelength, as described above, significantly decreases in the atmosphere, it is necessary to perform exposure in a decompressed space or a space purged with inert gas (e.g., N2 or He). Therefore, an exposure portion in an exposure apparatus is accommodated within a chamber whose environment is controlled.
To efficiently carry a wafer or reticle in and out of such a chamber, a load-lock mechanism is provided at an interface between an interior space and an exterior space. The load-lock mechanism includes a load-lock chamber and a gate valve capable of opening and closing communication between the load-lock chamber and each of the interior and exterior spaces.
For carrying the wafer or reticle out of the exterior space, the waver or reticle is first carried in the load-lock space in a state in which the load-lock chamber is isolated from the interior space. Then the load-lock chamber is decompressed or purged after the load-lock chamber is isolated from the exterior space. Then communication is established between the load-lock chamber and the interior space, and the wafer or reticle is carried in the interior space.
For carrying the wafer or reticle out of the interior space, the wafer or reticle is carried in the load-lock chamber in a state in which the load-lock chamber is isolated from the exterior space. Then the load-lock chamber is opened to atmosphere after the load-lock chamber is isolated from the interior space. Then communication is established between the load-lock chamber and the exterior space, and the wafer or reticle is carried to the exterior space.
The reticle is carried in and out while being contained in a reticle cassette in order to avoid dust from attaching to the reticle. Japanese Patent No. 3,320,628 discloses that, for carrying a sample in a vacuum processing chamber, a reticle cassette is carried in a load-lock chamber, the load-lock chamber is evacuated to a vacuum atmosphere, and the sample is then taken out of the reticle cassette.
When the reticle is taken out of the reticle cassette, dust is inevitably generated from a mechanism for opening and closing the reticle cassette. When the reticle cassette is opened and closed within the load-lock chamber, as described above, dust may rise during breakage of a vacuum of the load-lock chamber, and the dust may attach to a wall or ceiling of the load-lock chamber. The dust attaching to the ceiling or the like may fall onto the reticle taken out of the reticle cassette. This may cause common defects of an exposed device pattern or deteriorate flatness of the reticle, so that the quality of exposure may decline.
In the case where the reticle is taken out of the reticle cassette in the load-lock chamber and the reticle is stored in the vacuum processing chamber, because no protection of the reticle against dust is present, there is a possibility that the reticle is contaminated with the dust when being stored or conveyed.
In particular, if a vacuum of the vacuum processing chamber is broken when a problem occurs, dust in the vacuum processing chamber may rise and attach to the ceiling or the like, and the dust may fall onto the reticle. This may cause common defects of an exposed device pattern or deteriorate flatness of a reticle, so that the quality of exposure may decline.